Consider making throw and throwIO strict
It's possible for code to throw an exception that itself throws an imprecise exception. Such an exception is tricky to catch. For example:
import Control.Exception
strange = throwIO (undefined :: SomeException) `catch` \ex ->
case () of
_ | Just _ <- (fromException ex :: Maybe IOError) -> print "IOError"
| otherwise -> print "Something else"You might think that this would catch the exception and print "Something else", but in fact it does not. If others think this is as surprising as I do, perhaps we should make throwIO and throw strict, so an exception will never itself be bottom. Using
throwIO' !e = throwIO ein the code above instead of throwIO allows the exception to be caught.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.1 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Core Libraries |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |